The size of the House of Representatives, currently 435 members, is set by the Constitution (“The Number of Representatives shall not exceed one for every thirty Thousand, but each State shall have at Least one Representative”), and by the Apportionment Act of 1911 (2-page PDF) (62nd Cong, Sess. I, Chap. 5, H.R. 2983, Pub.L. 62-5, August 8, 1911), in effect since 1913, which established a limit of 433 and allowing for the addition of 2 more seats when Arizona and New Mexico were admitted into the Union in 1912. How the 435 seats are allocated among the states is determined after each decennial census in a process called “reapportionment,” 2 U.S.C. § 2A.

In the Constitution and in some documents and usage, these two separate bodies are referred to as “the two houses of Congress” or “both houses of Congress”. To avoid confusion, we prefer to use “two chambers of Congress” or “both chambers of Congress” rather than the more formal usage.

The other body: When members of the House and House staff speak of “the other body,” they are speaking of the Senate. When members of the Senate and Senate staff speak of “the other body,” they are speaking of the House.

A “Member of Congress” (MOC) can be a member of the House or the Senate.

At the national level there is only one legislative body formally known as the “House” and that is the U.S. House of Representatives. Currently the House has 435 members, and its members are called “Representative” (Rep.) or, colloquially, “Congressman” or “Congresswoman“.

Currently, there are 100 members of the U.S. Senate, and each member is called “Senator“.

Each “Congress” lasts for two years and is numbered as a “Term” of Congress. For example, the Congress meeting between January 3, 2017 and January 3, 2019 is the 115th Congress. Each term of Congress is divided into two Sessions, each session lasting one year. Being “in session” refers to when Congress is meeting during the session.

The Constitution provides that the Vice President of the United States is also the President of the Senate (Article I., Section 3.). Most of the time, a senator from the majority party in the Senate serves as the Senate’s presiding officer. When senators are speaking on the Senate floor, they address the presiding officer as “Mr. President.” In the contemporary Senate, when a female Senator is presiding, she is addressed as “Madame President.”

In the House, the presiding officer is the Speaker of the House (Article I., Section 2.). Often, a member of the House from the majority party in the House serves as the House’s presiding officer. When Representatives are speaking on the House floor, the form of address for the presiding officer depends on whether the House is sitting as the House (“Mr. Speaker” or “Madame Speaker”) or as the Committee of the Whole (“Mr. Chairman” or “Madame Chair”).

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